Carbon nanotubes are seamless, nanometer scale, single-walled or multiple-walled tubes of graphite sheets with fullerene caps. Single-walled carbon nanotubes (SWNTs) are generally either of the metallic-type or the semiconducting-type. SWNTs have shown promise for nanoscale electronics, chemical sensors, biological imaging, high strength materials, field emission arrays, tips for scanning probe microscopy, gas storage, photonics, and other important applications. The realization of the potential of SWNTs for these and other applications will likely depend on the availability of bulk quantities of SWNTs having uniform properties.
Most synthetic methods for producing SWNTs (arc and laser techniques, carbon vapor deposition, catalytic cracking of hydrocarbons, catalytic disproportionation of carbon monoxide, for example) result in mixtures of metallic and semiconducting SWNTs having a broad range of nanotube chiralities, diameters, and energy bandgaps. Mixtures of SWNTs are generally unsuitable for nanoscale electronics and other applications because the properties of SWNT mixtures are not uniform.